Gas transport properties of asymmetric polyimide membranes prepared by ion‐beam irradiation

Ion beam irradiation has been widely used to modify the structure and properties of membrane surface layers. In this study, the gas permeability and selectivity of an asymmetric polyimide membrane modified by He ion irradiation were investigated using a high vacuum apparatus equipped with a Baratron absolute pressure gauge at 76 cmHg and 35 °C. Specifically, we estimated the effects of the gas diffusion and solubility on the gas permeation properties of the asymmetric membranes with the carbonized skin layer prepared by ion irradiation. The asymmetric polyimide membranes were prepared by a dry–wet phase inversion process, and the surface skin layer on the membrane was irradiated by He ions at fluences of 1 × 10¹⁵ to 5 × 10¹⁵ ions/cm² at 50 keV. The increase in the gas permeability of the He⁺‐irradiated asymmetric polyimide membrane is entirely due to an increase in the gas diffusion, and the gas selectivity increases of the membranes were responsible for the high gas diffusion selectivities. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 262–269, 2007.     

Preparation and characterization of asymmetric polyethersulfone (PES) membranes

Flat‐sheet asymmetric polyethersulfone (PES) membranes were prepared from polyethersulfone (PES)/ polyethylene glycol (PEG)/ N‐methyl‐2‐pyrrolidone (NMP) system via phase inversion induced by immersion precipitation in water coagulation bath. Effects of propionic acid (PA) as a non‐solvent additive (NSA) on morphology and performance of the membranes prepared from PES/PEG 6000/NMP system in water coagulation bath were investigated. The cross section morphology of the membranes was studied by scanning electron microscopy (SEM). In addition, performance of the membranes was studied by water content measurements and separation experiments using pure water and human serum albumin (HSA) protein solution as feeds. According to SEM analysis, it was found out that the NSA has a significant influence on the structure of the skin layer and the sublayer. The obtained results indicated that addition of PA to the casting solution decreases permeation flux of the prepared membranes. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of asymmetric polyethersulfone membranes: effects of concentration and polarity of nonsolvent additives on morphology and performance of the membranes

In this study, effects of methanol, ethanol and 1‐propanol as variable nonsolvent additives (NSAs) on the morphology and performance of flat sheet asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from PES/Polyvinylpyrrolidone (PVP)/N‐methyl‐2‐pyrrolidone (NMP) system via phase inversion. The obtained results indicate that with the addition of NSAs to the casting solution, the membrane morphology changes slowly from macrovoids to an asymmetric structure with finger‐like pores. By increasing the NSAs concentrations in the casting solution and decreasing their polarities, the membrane structure changes from finger‐like pores to sponge. The AFM and SEM images reveal that addition of NSA to the casting solution decreases the pore size of the prepared membranes and reduces the pure water flux and BSA solution flux, while increasing the protein rejection. Surface analysis of the membranes showed that mean pore size and surface porosity of the prepared membranes with NSAs in the casting solution are smaller compared with those of the membrane prepared with no NSA. Pure water flux and BSA solution flux through the membranes decrease and BSA rejection increases with increase in the concentration of NSAs and decrease in their polarity. Finally, it can be concluded that the T_g values of the PES membranes increase by addition of NSAs to the casting solution. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared spectroscopic studies of CO2 sorbed in glassy and rubbery polymeric membranes

Infrared spectra of CO₂ sorbed in rubbery and glassy polymers were measured to examine the relationships between the spectroscopic data and physical properties of the polymeric membranes. The “V-shape” tendency in the plot of W₁ [i.e., half-width of CO₂ peak sorbed in the membranes] vs glass-transition temperature (T_g) is observed, and has exactly the same tendency that is widely known from the plot of log D (diffusion coefficient) vs T_g. It is suggested that the membranes having a wider W₁ give a faster diffusion coefficient, since W₁ is inversely related to the moment of inertia of CO₂ in the membranes. Two distinct peaks of CO₂ were not observed in the infrared spectra of CO₂ sorbed in the glassy polymers. This suggests that the states of CO₂ in the Henry mode and Langmuir mode in the glassy polymers are similar in the spectroscopic measurements. © 1994 John Wiley & Sons, Inc.     

Modification of polyethersulfone membranes using terpolymers engineered and integrated antifouling and anticoagulant properties

In this study, random terpolymers of methoxy poly(ethylene glycol)‐poly(sodium styrene sulfonate‐co‐methyl methacrylate) (MPEG‐P(SSNa‐co‐MMA)) integrated with antifouling and anticoagulant properties were synthesized by atom transfer radical polymerization (ATRP) for the first time and confirmed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC). The terpolymers with desired antifouling and anticoagulant segments were then used as amphiphilic additives to modify polyethersulfone membranes by an engineering blended approach. Water contact angle (WCA) results indicated that the surface hydrophilicity of the modified membranes enhanced. Protein ultrafiltration experiments showed that the antifouling ability of the modified membranes increased. In addition, the modified membranes showed decreased protein adsorption (bovine serum albumin, BSA), suppressed platelet adhesion, and prolonged activated partial thromboplastin time (APTT). Copyright © 2013 John Wiley & Sons, Ltd.     

Gas permeation through water-swollen hydrogel membranes

This work deals with water-swollen hydrogel membranes for potential CO₂ separation applications, with an emphasis on elucidating the role of water in the membrane for gas permeation. A series of hydrogel membranes with a wide range of water contents (0.9–10 g water/g polymer) were prepared from poly(vinyl alcohol), chitosan, carboxyl methyl cellulose, alginic acid and poly(vinylamine), and the permeation of CO₂, H₂, He and N₂ through the membranes at different pressures (200–800 kPa) was studied. The gas permeabilities through the dry dense membranes were measured as well to evaluate the resistance of the polymer matrix in the hydrogel membranes. It was shown that the gas permeability in water-swollen membrane is lower than the gas permeability in water, and the selectivity of the water-swollen membranes to a pair of gases is close to the ratios of their permeabilities in water. The permeability of the water-swollen membranes increases with an increase in the swelling degree of the membrane, and the membrane permeability tends to level off when the water content is sufficiently high. A resistance model was proposed to describe gas permeation through the hydrogel membranes, where the immobilized water retained in the polymer matrix was considered to form transport passageways for gas permeation through the membrane. It was shown that the permeability of hydrogel membranes was primarily determined by the water content in the membrane. The model predictions were consistent with the experimental data for various hydrogel membranes with a wide range of water contents (0.4–10 g water/g polymer).     

Gas transport properties of polypropylene/clay composite membranes

Polypropylene membranes modified with natural and organically modified montmorillonite clays were prepared. The permeability, diffusivity and solubility of helium, oxygen and nitrogen were determined for the unfilled and filled membranes over the temperature range 25-65 °C. Physical properties of polypropylene membranes were investigated using X-ray diffraction, thermogravimetric analyser, tensile testing and differential scanning calorimetry. The results showed that the filled membranes exhibit lower gas permeability compared to the unfilled polypropylene membrane. For helium, a reduced diffusivity is mainly responsible for the reduction in the permeability, in contrast, for nitrogen and oxygen, both diffusivity and solubility were reduced by the presence of fillers. The X-ray diffraction spectra showed that the incorporation of the unmodified and modified clay did not affect the crystallographic nature of polypropylene.     

Halo formation in asymmetric polyetherimide and polybenzimidazole blend hollow fiber membranes

For the first time, we have reported a halo (ring) formation occurred in the cross‐section of integrally skinned asymmetric membranes. These membranes were wet‐spun from solutions containing 30 and 33 wt % of 95/5 and 90/10 polyetherimide (PEI)/polybenzimidazole (PBI). Both Imaging X‐ray Photoelectron Spectroscopy (XPS) and Dynamic Mechanical Analyzer's (DMA) data suggest PEI and PBI form miscible blends the “halo” is not chemically different from the matrix and is most likely a physical phenomenon of unique pore morphology. In other words, uniform porosity was created in the middle of hollow fiber cross‐section area, which performs as a filter for light transmission. We found that the addition of PBI in PEI/DMAc solution not only depresses the macrovoid formation, but also changes the precipitation path: nucleation growth vs. spinodal decomposition. The formation of a halo within a membrane is possibly due to the fact that a uniform nucleation growth occurs in the ring region during the early stage of phase separation because of high solution viscosity and diffusion controlled solvent‐exchange process, and then separation grows in the mechanism of spinodal decomposition from small amplitude composition fluctuations. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1575–1585, 1999     

Gas transport properties of asymmetric polyimide membranes prepared by plasma‐based ion implantation

In this study, we report the gas permeance and selectivity of the asymmetric polyimide membrane prepared by plasma‐based ion implantation (PBII). The asymmetric polyimide membranes were prepared using a dry–wet phase inversion process, and the surface skin layer on the membrane was implantated by He ions at 2.5 keV. The asymmetric membranes treated by PBII were measured using a high vacuum apparatus with a Baratron absolute pressure gauge at 76 cmHg and 35°C. The (O₂/N₂) and (CO₂/CH₄) selectivities in the He⁺‐implanted asymmetric membrane at 60 sec resulted in 1.5 and 1.8 time increases, respectively, when compared to those of the asymmetric membrane before PBII. On the other hand, the O₂ and CO₂ permeances in the asymmetric membrane after PBII decreased with an increase in the He⁺ treatment time. In this paper, we addressed, for the first time, the gas permeation behavior of the asymmetric polyimide membranes prepared by PBII. Copyright © 2009 John Wiley & Sons, Ltd.     

Improved microfiltration and bacteria removal performance of polyethersulfone membranes prepared by modified vapor‐induced phase separation

Polyethersulfone (PES) microfiltration membranes were fabricated by a combined vapor‐induced phase separation and wet phase separation method. The effect of different non‐solvent additives in casting solution, ie, acetone, diethylene glycol, and triethylene glycol (TEG) was investigated on the membrane morphology and performance. Scanning electron microscopy images showed that the membrane containing TEG additive had a skinless symmetric structure with well interconnected pores. The permeability of the PES/PVP/TEG membranes increased by decreasing PES and TEG and increasing PVP concentration. Bacteria removal performance of the prepared membranes was investigated by the filtration of E. coli suspension. The membrane made from casting solution containing 15 wt.% PES, 16 wt.% PVP, and 20wt.% TEG showed a pure water flux of ~ 5370 L/m² h at low transmembrane pressure of 10 psi and 100% bacteria removal efficiency. The results of in vitro cytotoxicity test and cell viability assay showed non‐toxic nature of the prepared membranes.     

Effect of type of solvent and non‐solvents on morphology and performance of polysulfone and polyethersulfone ultrafiltration membranes for milk concentration

Polysulfone (PS) and polyethersulfone (PES) ultrafiltration membranes were manufactured from a casting solution of the polymer, polyvinylpyrrolidone (PVP) in various solvents [N,N‐dimethylacetamide (DMAc), N,N‐dimethylformamide (DMF) and 1‐methyl‐2‐pyrrolidone (NMP)] by immersing the prepared films in different non‐solvents [water, 2‐butanol, mixture of water and 2‐butanol, mixture of water and 2‐propanol (IPA) and mixture of water and 1‐butanol]. The influences of various solvents and non‐solvents on morphology and performance of the prepared membranes were analyzed by scanning electron microscopy (SEM) and separation experiments using milk as the feed. Copyright © 2005 John Wiley & Sons, Ltd.     

Ammonia and carbon dioxide permeability through perfluorosulfonic membranes

Transmembrane transport of ammonia and carbon dioxide through perfluorosulfonic membranes in ionic forms of transition metals was studied in a wide temperature interval. The different patterns of the temperature plots of the permeability coefficient of ammonia were found for different ionic forms of the membrane. An increase in the ammonia permeability with an increase in the moisture contents of the membrane also depends on its ionic form. The effects observed are explained by the different structures of water—ammonia complexes formed with metal ions. The mechanism of transmembrane transport of ammonia through perfluorosulfonic membranes in various ionic forms is discussed.     

Tailoring polyethersulfone/quaternary ammonium polysulfone ultrafiltration membrane with positive charge for dye and salt selective separation

Polyethersulfone (PES)/quaternary ammonium polysulfone (QAPSf) blend ultrafiltration (UF) membranes with positive charge were fabricated by nonsolvent induced phase separation (NIPS) for use in dye and salt selective separation. QAPSf was synthesized by nucleophilic substitution with chloromethylated polysulfone (CMPSf). The effect of the PES/QAPSf mass ratio on the morphology and performance of blend UF membranes were studied. The membranes' zeta potentials gradually changed from negative to positive with decreases in the PES/QAPSf mass ratio. At PES/QAPSf mass ratios of 30:70 and 10:90, the zeta potentials of the membranes reached +1.8 mV and + 5.9 mV, respectively. Additionally, the contact angles of the membranes decreased from 74° to 52° as the QAPSf content increased from 0 wt% to 90 wt%. Furthermore, the membrane with a PES/QAPSf mass ratio of 30:70 showed a high water permeance (181.4 LMH bar⁻¹) and excellent dye and salt selective separation performance. The rejection ratios reached 99.1%, 87.8%, 99.6%, and 92.4% for dyes Congo red, methyl blue, Alixin blue 8GX, and basic blue 24, respectively, while those for salts Na₂SO₄, MgSO₄, MgCl₂, and NaCl were ≤ 10%. In addition, the PES/QAPSf membranes showed excellent antifouling performance and good operating stability with dye-salt mixtures of various pHs and salt concentrations.     

Palladium magnetic nanoparticle‐polyethersulfone composite membrane as an efficient and versatile catalytic membrane reactor

Developing polymer catalytic membrane reactors is an aim due to its outstanding advantages. In this paper, a novel catalytic membrane containing palladium‐supported magnetic nanoparticles is introduced. Silica‐iron oxide core shell nanoparticles were first prepared and functionalized by phosphine ionic liquid functionalized poly(ethylene glycol). The modified magnetic nanoparticles were used as support for immobilization of palladium. The final palladium‐immobilized nanoparticles were used as active filler for the preparation of membrane reactor. The prepared membranes were characterized, and their activities were tested in carbon‐carbon bond formation and catalytic reduction. The catalytic membrane showed good performance in the mentioned reactions.     

Gas transport in polyurethane-polystyrene interpenetrating polymer network membranes. I. Effect of synthesis temperature and molecular structure variation

The gas (oxygen and nitrogen) transport characteristics of the interpenetrating polymer network (IPN) membranes of polyurethane/polystyrene were studied. The effect of synthesis temperature, composition, molecular weight of the polyol and aromatic content (of MDI, TDI and HDI) on the gas permeability were analyzed. In the IPN synthesis, first polyurethane was polymerized thermally, and then polystyrene was polymerized by photolytic methods at different temperatures. The permeability coefficient decreased and the separation factor increased with decreasing synthesis temperature due to the miscibility increase. The permeability coefficient showed a minimum value and the separation factor showed a maximum value at ca.25 wt.% polyurethane composition. The permeability coefficient decreased and the separation factor increased with increasing aromatic content in polyurethane component. The morphology and density behavior of the IPN's agreed well with the permeability data. The tensile strength of the membrane increased with decreasing synthesis temperature and with increasing crosslink density and polystyrene content.     

Tunning CO2 Separation Performance of Ionic Liquids through Asymmetric Anions

This work aims to explore the gas permeation performance of two newly-designed ionic liquids, [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂], in supported ionic liquid membranes (SILM) configuration, as another effort to provide an overall insight on the gas permeation performance of functionalized-ionic liquids with the [C₂mim]⁺ cation. [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂] single gas separation performance towards CO₂, N₂, and CH₄ at T = 293 K and T = 308 K were measured using the time-lag method. Assessing the CO₂ permeation results, [C₂mim][CF₃BF₃] showed an undermined value of 710 Barrer at 293.15 K and 1 bar of feed pressure when compared to [C₂mim][BF₄], whereas for the [C₂mim][CF₃SO₂C(CN)₂] IL an unexpected CO₂ permeability of 1095 Barrer was attained at the same experimental conditions, overcoming the results for the remaining ILs used for comparison. The prepared membranes exhibited diverse permselectivities, varying from 16.9 to 22.2 for CO₂/CH₄ and 37.0 to 44.4 for CO₂/N₂ gas pairs. The thermophysical properties of the [C₂mim][CF₃BF₃] and [C₂mim][CF₃SO₂C(CN)₂] ILs were also determined in the range of T = 293.15 K up to T = 353.15 K at atmospheric pressure and compared with those for other ILs with the same cation and anion’s with similar chemical moieties.     

The effects of polymer chain rigidification, zeolite pore size and pore blockage on polyethersulfone (PES)-zeolite A mixed matrix membranes

The polyethersulfone (PES)-zeolite 3A, 4A and 5A mixed matrix membranes (MMMs) were fabricated with a modified solution-casting procedure at high temperatures close to the glass transition temperatures (T_g) of polymer materials. The effects of membrane preparation methodology, zeolite loading and pore size of zeolite on the gas separation performance of these mixed matrix membranes were studied. SEM results show the interface between polymer and zeolite in MMMs experiencing natural cooling is better (i.e., less defective) than that in MMMs experiencing immediate quenching. The increment of glass transition temperature (T_g) of MMMs with zeolite loading confirms the polymer chain rigidification induced by zeolite. The experimental results indicate that a higher zeolite loading results in a decrease in gas permeability and an increase in gas pair selectivity. The unmodified Maxwell model fails to correctly predict the permeability decrease induced by polymer chain rigidification near the zeolite surface and the partial pore blockage of zeolites by the polymer chains. A new modified Maxwell model is therefore proposed. It takes the combined effects of chain rigidification and partial pore blockage of zeolites into calculation. The new model shows much consistent permeability and selectivity predication with experimental data. Surprisingly, an increase in zeolite pore size from 3 to 5 Å generally not only increase gas permeability, but also gas pair selectivity. The O₂/N₂ selectivity of PES-zeolite 3A and PES-zeolite 4A membranes is very similar, while the O₂/N₂ selectivity of PES-zeolite 5A membranes is much higher. This implies the blockage may narrow a part of zeolite 5A pores to approximately 4 Å, which can discriminate the gas pair of O₂ and N₂, and narrow a part of zeolites 3A and 4A pores to smaller sizes. It is concluded that the partial pore blockage of zeolites by the polymer chains has equivalent or more influence on the separation properties of mixed matrix membranes compared with that of the polymer chain rigidification.     

Structure and gas permeability of asymmetric polyimide membranes made by dry–wet phase inversion: Influence of alcohol as casting solution

In this article, we have reported the influence of alcohol as a casting solution on the structure and the gas permeability of asymmetric polyimide membranes made by dry–wet phase inversion. The apparent skin layer thickness of the asymmetric membrane decreased with an increase in molecular weight of the alcohol, and the thicknesses of the membranes made from methanol, ethanol, propanol, and butanol were 250, 120, 61, and 31 nm, respectively. We found that χ₁₂ as an interaction parameter of solvent–nonsolvent had a significant influence on the phase inversion occurring in the coagulant medium. On the other hand, the gas permeance and the gas selectivity in the asymmetric membranes increased with the increasing molecular weight of the alcohol. We believe that a more packed structure formed in the asymmetric polyimide membrane with a thinner surface skin layer is also responsible for the thickness‐dependence of the gas selectivity obtained in this study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2739–2746, 2007     

Effect of annealing on the morphology and properties of poly(lactic acid)/polyhedral oligomeric silsesquioxane asymmetric porous membranes prepared through non-solvent induced phase separation and its application

Non-solvent induced phase separation (NIPS) method was employed to fabricate biodegradable poly(lactic acid) (PLA) nanocomposite membranes. Morphological studies using scanning electron microscopy revealed that all the membranes prepared display asymmetric structures comprising finger-like macropores. The incorporation of modified polyhedral oligomeric silsesquioxane (POSS) particles into the PLA matrix resulted in enhanced crystallinity, mechanical, and thermal properties. Annealing of the membranes was performed to explore the influence of temperature on the morphology and properties. After annealing, membranes become more thin and compact, and drastic enhancement in crystallinity is also observed. Consequently, Young's modulus experiences a significant improvement. The reduction in oil absorption capacity after annealing can be attributed to the higher level of crystallinity, reduced porosity, and smaller pore diameter observed in the annealed membranes. Additionally, the unannealed PLA nanocomposite membranes demonstrated exceptional oil absorption capacity, reaching approximately 88%. It is foreseeable that these PLA/POSS nanocomposite membranes possess the potential to be utilized as effective tools for oil–water separation, offering the advantage of mitigating secondary pollution.     

Recent advances in polymeric facilitated transport membranes for carbon dioxide separation and hydrogen purification

Membrane and membrane process have been widely considered as one of the best candidates for mitigating CO₂ emissions from the combustion or utilization of fossil fuels. Various amine-containing polymers constitute an important class of membranes, where the highly selective CO₂ transport is achieved by the facilitated transport mechanism. In this review, the amine–CO₂ chemistry is discussed in conjunction with the mechanism of the reaction-mediated CO₂ transport. A wide variety of amine-containing polymers are discussed based on two synthesis motifs: (a) polyamines with amino groups covalently bound to the polymer backbone and (b) small molecule amines embedded in a polymer matrix. This review concludes with the remarks on the facilitated transport membranes for post-combustion carbon capture (CO₂/N₂) and hydrogen purification (CO₂/H₂).